The present invention relates to a simplified low cost jet pump, and to a jet propelled watercraft utilizing said pump.
Some sports and occupations, such as fishing, require a boat that is highly maneuverable and capable of use in shallow waters and the like. Jet powered boats are considered to be generally superior to propeller driven boats for such service, but the complexity and cost of conventional jet drives for jet propelled boats have limited use of such watercraft.
In general, conventional jet propulsion systems for small watercraft require an opening in the bottom of the craft which serves as a water intake, a pump for pressurizing the water entering through the intake opening, and a discharge tube extending from the pump through the stern wall or transom of the watercraft. The water passes from the discharge tube as a jet and exerts force on the jet propulsion system to drive the watercraft through the water. A typical watercraft of this type is described in U.S. Pat. No. 3,426,724 of Jacobson entitled Power Driven Aquatic Vehicle.
Jet propulsion of boats is inherently less efficient than propeller driven boats, and as a result has been limited in use to small personal watercraft, such as described in U.S. Pat. No. 3,426,724, or relatively large pleasure craft, both of which are relatively expensive. Further, neither small personal watercraft nor large pleasure craft is desirable for those sports and occupations requiring highly maneuverable boats and boats capable of use in shallow waters.
One of the reasons for the high cost of such watercraft is the cost of marine engines to drive the watercraft. In addition, marine engines are expensive to maintain. A major reason that marine engines are costly is low production. Since relatively few marine engines are produced, the cost of design and parts remains significantly higher than those of general utility engines, such as those used for lawn mowers, water pumps, rail splitters, and the like.
Another reason for the high cost of marine engines is the hostile environment in which they operate. Not only must such engines operate in a moist environment, but they are cooled by water drawn from the body of water upon which they operate, and this water may contain plant matter and/or minerals that adhere to the surfaces of the cooling system and make maintenance costly. Further, the use of external water for cooling requires the engine to employ special materials in its cooling system.
Most marine engines used for small watercraft are two-cycle engines that are inherently smaller, lighter and less costly to construct than four-cycle engines, and therefore particularly adapted for low production requirements. Two-cycle engines, however, are less efficient than four-cycle engines. Further, two-cycle engines develop their horse power at higher revolution rates than four-cycle engines, and therefore tend to be noisier. Two-cycle engines are also less convenient to use than four-cycle engines, since they require oil to be mixed with the fuel for the engine. Further, the use of two-cycle engines creates more pollution of the environment than use of four-cycle engines because vapors from the oil in the fuel are expelled into the atmosphere or water. Environmental considerations have caused the boating industry to consider the use of four-cycle engines rather than two-cycle engines even for small personal watercraft and has resulted in special marine four-cycle engines, such as described in U.S. Pat. No. 5,846,102 entitled FOUR-CYCLE ENGINE FOR A SMALL JET BOAT.
It is a general object of the present invention to provide a highly maneuverable boat that preferably is capable of use in shallow waters. It is a farther object of the present invention to provide such a boat at a significantly reduced cost from that of conventional constructions. More specifically it is an object of the present invention to provide a jet propelled boat that utilizes an air cooled four-cycle engine, and which may be constructed at a significantly lower cost than conventional comparable boats.
It is a further object of the present invention to provide a jet pump and engine assembly with the rotating member of the pump directly mounted on the drive shaft of the engine, thereby eliminating the mechanical coupling devices, bearings, support structure and seals which are generally used between the engine drive shaft and the rotating member of the pump. In the inventor's preferred construction, the drive shaft seal of the engine confronts the rotor of the pump, and the pump uses an impeller mounted on the rotor and disposed within a chamber to drive the liquid toward the engine seal, thereby pressurizing the liquid within the chamber and, in the absence of a remedial device, subjecting the seal to operating conditions that tend to damage the engine seal. It is a further object of the present invention to provide an assembly of an engine and a pump in which the pump has an impeller disposed within a chamber and directly mounted on the drive shaft of the engine, the impeller driving liquid toward the drive shaft seal of the engine, and the pump being provided with means to reduce or eliminate the pressure of the liquid being operated upon at the drive shaft seal.
Directly mounting a rotor of a pump on the drive shaft of an engine has the potential disadvantage of placing a force on the drive shaft that is directed along the axis of the drive shaft. Since in the preferred embodiment, the rotor has an impeller that transports liquid towards the bearing on the engine drive shaft, the drive shaft must provide the counter force to retain the drive shaft in position within the engine. It is a further object of the present invention to provide means associated with the rotor of the pump for reducing or eliminating the force on the drive shaft that is produced by the impeller.